Unifor Local 195 members with Jamieson Laboratories are heading to the picket lines.
At the union hall this morning, 57% of workers voted against a tentative agreement. The tentative deal was reached late on Tuesday.
Local president Gerry Farnham telling AM800 News at the time, the deal was reached just before the strike deadline set at midnight.
"The bargaining committee is obviously happy to have reached a tentative agreement, I mean we're bringing it right down to the wire, 15 minutes prior to the possibility of strike action," says Farnham.
The union represents about 240 workers at the plant which are now officially on strike.
More to come.